The Galactic Halo in Mixed Dark Matter Cosmologies

TL;DR

This study uses high-resolution simulations to explore how mixed cold and warm dark matter components affect the Milky Way halo, revealing that local WDM fractions vary with particle mass and impact dark matter search interpretations.

Contribution

It introduces a correction formula for local dark matter fractions in mixed models, challenging the assumption that local and cosmic dark matter ratios are identical.

Findings

Local WDM fraction depends strongly on WDM particle mass for masses below 1 keV.

Using the standard scaling ansatz can lead to significant errors in dark matter search interpretations.

A simple formula is provided to accurately estimate local dark matter densities for mixed dark matter models.

Abstract

A possible solution to the small scale problems of the cold dark matter (CDM) scenario is that the dark matter consists of two components, a cold and a warm one. We perform a set of high resolution simulations of the Milky Way halo varying the mass of the WDM particle ($m_{\rm WDM}$) and the cosmic dark matter mass fraction in the WDM component ($\bar{f}_{\rm W}$). The scaling ansatz introduced in combined analysis of LHC and astroparticle searches postulates that the relative contribution of each dark matter component is the same locally as on average in the Universe (e.g. $f_{\rm W,\odot} = \bar{f}_{\rm W}$). Here we find however, that the normalised local WDM fraction ($f_{\rm W,\odot}$ / $\bar{f}_{\rm W}$) depends strongly on $m_{\rm WDM}$ for $m_{\rm WDM} <$ 1 keV. Using the scaling ansatz can therefore introduce significant errors into the interpretation of dark matter searches. To correct this issue a simple formula that fits the local dark matter densities of each component is provided.